The present invention relates to the art of selective nerve stimulation. The invention finds particular application in conjunction with urination control and will be described with particular reference thereto. The invention is also applicable to control other aspects of the nervous system, such as for fecal incontinence, penile erection, and others.
The organs involved in bladder, bowel, and sexual function receive much of their control via the second, third, and fourth sacral nerves, commonly referred to as S2, S3 and S4 respectively. Electrical stimulation of these various nerves has been found to offer some control over these functions. Several techniques of electrical stimulation may be used, including stimulation of nerve bundles within the sacrum.
The sacrum, generally speaking, is a large, triangular bone situated at the lower part of the vertebral column, and at the upper and back part of the pelvic cavity. The spinal canal runs throughout the greater part of this bone. It lodges the sacral nerves, and is perforated by the anterior and posterior sacral foramina through which these pass out.
Several systems of stimulating sacral nerves exist. For example, U.S. Pat. No. 4,607,639 to Tanagho et al. entitled "Method and System for Controlling Bladder Evacuation", incorporated herein by reference, and the related U.S. Pat. No. 4,739,764 to Lue et al. entitled "Method for Stimulating Pelvic Floor Muscles for Regulating Pelvic Viscera", also incorporated herein by reference, disclose implanting an electrode on at least one nerve controlling the bladder. In one embodiment the electrode is percutaneously implanted through the dorsum and the sacral foramen of the sacral segment S3 for purposes of selectively stimulating the S3 sacral nerve. The electrode is positioned using a hollow spinal needle through a foramen (a singular foramina) in the sacrum. The electrode is secured by suturing the lead body in place. U.S. Pat. No. 4,569,351 to Tang entitled "Apparatus and Method for Stimulating Micturition and Certain Muscles in Paraplegic Mammals", incorporated herein by reference, discloses use of electrodes positioned within the sacrum to control bladder function.
Typically electrical stimulation of the nerves within the sacrum is accomplished by positioning a lead having at least one electrode at its distal end through a foramen of the sacrum and proximate the nerve. Not all patients, however, are suitable for such stimulation. In fact, at present there is not a reliable screening tool to identify patients who would or would not benefit from sacral nerve stimulation other than to actually stimulate such nerves.
Placing a lead into the sacrum in order to assess the efficacy of sacral nerve stimulation may be performed percutaneously, that is, simply using a needle. Leads implanted in such a manner, however, have to date been difficult to reliably anchor so that the electrode remains in the correct position. Techniques such as taping the exterior lead body to the patient are not wholly satisfactory in terms of both the electrode placement as well as patient comfort. Other techniques which are effective to anchor a sacral lead, such as screwing the lead to the sacral bone, are much too invasive for an initial screening procedure. An additional method of anchoring such a lead may be seen in the pending U.S. patent application Ser. No. 08/811,054 of Moumane et al., "Sacral Medical Electrical Lead" filed Mar. 3, 1997 assigned to the assignee of the present invention and incorporated herein by reference. That application generally concerned a sacral lead which had a notched section in which the insulation of the lead body presents a macroscopically roughened surface to engage into tissue without causing damage to the tissue. One drawback to this design, however, is that any pulling or tugging on the proximal end of the lead body outside the body could be directly communicated to the electrode section, thus creating a higher likelihood of electrode dislodgment and poor stimulation.
Thus there exits a need for a medical electrical lead which may be safely and effectively implanted into the sacrum and anchored within in a minimally invasive manner, but which further prevents any pulling or tugging on the proximal end of the lead body outside the body to be directly communicated to the electrode.